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Friday, January 30th 2009, 4:27pm

Anti siphon

If I use anti siphon valves, why do i have to use a back flow device?

What the difference between a master valve, and the other ones. I have read that master valves are not always necessary.


Supreme Member

Posts: 482

Location: Houston, Texas


Saturday, January 31st 2009, 12:21pm

It will all depend on the application. What are you watering? how are you watering are there any hazards? What kind of Hazard of contamination, chemicals, pumps. This will help determine you required backflow prevention device in addition to your local water authorities requirement.

Master valve designation is identical in material. It is the same valve, but it is located in the sprinkler system before all of the other valves, but after your backflow prevention device.


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Supreme Member

Posts: 5,323

Location: Metro NYC


Monday, February 2nd 2009, 9:09am

By the way, there is no such thing as a Master Antisyphon Valve.


Supreme Member


Friday, February 6th 2009, 9:39am

Anti siphon values, when installed correctly, is your back flow device.

BUT, the big question is whether your local building codes will permit them. Based on what I've read in this and similar forums over the years, building codes vary widely on what is allowed back flow devices for a sprinkler system. Some locations specify the back flow device down to the part number, others are as lax as to only indicate "some sort of backflow".

There is nothing special about a master valve other than it's placement. If you design a system using in-line valves (as opposed to anti-siphon valves), you would purchase the same valve for the master valve as you would for the individual circuit valves. A master valve is a valve installed upstream from the manifold. It's basic idea is that it serves as a sort of backup valve in case your sprinkler valve ever gets stuck in the "open" position. (The idea is that you will only waste water if BOTH the master valve and circuit valve both become stuck). There are other reasons to use (and some would say NOT use) a master valve, and a master valve is not REQUIRED unless your building codes require one.

And what I believe the points Wet_Boots' statement is making is that:
1. If you are using anti-siphon valves AND a master valve, the master valve should be a regular inline valve and NOT an anti-siphon valve.
2. You can not use an anti-siphon valve as your master valve and inline valves for your manifold and think you are covered as far as back-flow. The anti-siphon valve will not properly function as a back flow device in this arrangement. If this is the type of setup you want to use, then rather than an anti-siphon valve for a master valve, you should use a PVB back flow device followed by an inline master valve. With a PVB properly installed, you don't need/want anti-siphon valves.

Other things to note is that your application can effect what type of back flow device is needed. As an example, if you attempt to use fertigation (injecting fertilizer into the irrigation system), that sort of system REQUIRES an RPZ for a back flow device.




Friday, February 6th 2009, 10:47am


I would prefer to use inline valve no mater, and a PVB. Seems simple that way.

Thanks for the great information.


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